To determine the concentration of iron ions in a water sample collected from a local lake using the polarography technique, you would need to follow these steps:1. Collect a water sample from the lake.2. Prepare the sample by filtering it to remove any suspended particles and debris.3. Perform a calibration using a series of standard solutions containing known concentrations of iron ions. This will help you establish a calibration curve.4. Analyze the water sample using a polarographic instrument, such as a voltammetric analyzer or a polarograph.5. Record the current response peak height or area of the iron ions in the water sample.6. Compare the current response of the water sample to the calibration curve to determine the concentration of iron ions in the sample.Please note that without the actual data from the polarographic analysis, it is not possible to provide a specific concentration value for the iron ions in the water sample.